1. Field of the Invention
The present invention relates to an improved device for measuring the intensity of the light scattered by high concentrations of particles or macromolecules of a size ranging between a few nanometers and several hundred nanometers. It more particularly applies to the correlation of photons in liquid media.
2. Description of the Prior Art
Document EP-0,654,661 A1 describes light scattering measurements performed on a thin film by a first dioptric interface and a measuring finger. FIG. 1 is a cross-sectional view of the device according to this prior document. It comprises a prism P, of angle A=90°, for totally reflecting a laser beam L. The faces of the prism form a diopter, which is an optical surface separating two media of different refractive indices. The laser beam enters through face E which is totally reflected by secant face F which exits through the normal of face S. Face S is topped by a part N with a channel therethrough defining a tank for receiving a volume of a sample containing objects M to be analyzed. The device also comprises a micropositioner G holding a bar H carrying at one end thereof a black glass rod D for limiting the reflected or scattered light intensity to prevent a parasitic intensity from reaching photodetector I. Advantageously, rod D has a (convex) radius of curvature for selectively providing a film as thin as possible for creating an analysis zone of the order of 1 mm2.
However, this device has drawbacks:
Rod and/or prism surface damage occurs after several uses which is likely to lead to artifacts due to the intensity of light which is scattered by these micro-scratches that appear over time.
The convex finger is delicate to manufacture in view of the polishing operation (Lambda/4 tolerance) being difficult for curved shapes which significantly increases the cost of this part,
The black rod can cause residual reflectivities that interfere in the measurement.
It is impossible to perform a measurement under flow without the latter disturbing the measurement due to the small surface of contact of the rod.